Search by Document Profile in SharePoint 2003

In SharePoint 2001 you could limit your search to documents that used a particular profile. Obviously, this breaks down in 2003 but I have a client that upgraded to 2003 using the Backward Compatible Document Library and they are looking for this functionality. Does anyone have an idea how this might be accomplished in 2003? If this is one of the properties that can be added I'm not seeing it

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